This invention relates generally to fasteners and, in particular, to screws and nuts having a self fastening feature.
The purpose of a self fastening feature in a screw or nut is to prevent undesired loosening of the screw or nut from engagement in a workpiece as a result of vibration and other factors. In the art, the primary self locking vehicle is a lockwasher positioned intermediate the head of the screw or nut and the surface of a workpiece. The lockwasher may be provided with teeth of various configurations which engage the surface of the workpiece to hold the screw or nut.
The "teeth" on the lockwasher are usually deformable during engagement to provide a bias on the screw threads and to increase the holding forces tending to hold a screw in position. Lockwashers have proved less than completely satisfactory because of the expense of separate parts and the use thereof and because of the possibility of some relative rotation between the lockwasher and the screw or nut, the screw or nut not being affirmatively held. A variation in the use of lockwashers is to capture a lockwasher on the body of the screw adjacent the head or on the nut. The lockwasher is still displaceable relative to the screw or nut and this arrangement has likewise not proved completely satisfactory.
In the art, it has been proposed to form tabs in flanges projecting radially from the head of a screw to serve the lockwasher function. Thus, in U.S. Pat. No. 2,226,491, it is proposed to twist a dome shaped flange (FIGS. 4-6) or a planar flange (FIGS. 7-9). In the former case the dome shape of the tabs prevents proper distortion during use while the planar tabs provide insufficient retaining force. In U.S. Pat. No. 3,343,580, it is proposed to twist a planar flange so that the lowermost projections of the tab define a sinusoidal envelope, an arrangement that does not provide maximum uniform force.
In U.S. Pat. No. 4,350,465 of the applicant herein, a spider washer head screw is disclosed and in U.S. patent application Ser. No. 800,198 of the applicant herein, a spider washer head nut is disclosed. Applicant hereby incorporates the teachings of his prior patent and of his prior application by reference as if fully set forth herein. These self locking screws and nuts are effective and avoid many of the deficiencies of the prior art. However, in certain situations, such screws and nuts are not useful because the screw or nut is stripped during tightening as a result of insufficient torque absorption.
By providing spider washer head fasteners having flanges integrally formed with the body of a screw or nut as more particularly described below, the deficiencies of the prior art have been avoided and new and highly effective screws and nuts are provided.